connect an electrical circuit to the microphone input

Hello,

I have designed a waveform display program to act as an oscilloscope for home use that can handle electrical signals from circuits when these signals are fed into the soundcard .

I first have to bring down signal voltages to a safe level of about 1 - 2V (AC). I have done this using a voltage divider arrangement.

when I feed this voltage to the soundcard (microphone port), no output is displayed. When i connect a microphone however and speak into it, a waveform is displayed. In addition I wrote a function generator (sine, square etc), and when this program is ran, if its output collected from the "speaker out" port (on the soundcard) is fed into the "microphone in" port (on the soundcard) it is correctly plotted on the display program.

I measured the output voltage from microphones, it is about 1 - 2 v so I am wondering why the 1V from microphones show a waveform whereas the 1 - 2V from external circuits does not. I guess this is an impedance matching problem, but I am not sure of what to do further. I would like to know how to make my signal compatible with that from the microphes so that it can be plotted too. Any idea is appreciated ! Thanks .

It would not be an impedance matching problem unless your source has a very high impedance.

Can you read the voltage from the source with a voltmeter? If so, connect a 47k resistor across the meter and observe the decrease in the reading. This will give you an indication of the output resistance of the source. If you are unable to calculate the output resistance, post the results of your measurements and I'll do it for you.

1 Volt output from a microphone seems rather large. Did you measure this with a meter or an oscilloscope?

Perhaps your source is overloading the input. If that was the case, you should be able to see it in the recorded data.

Len

well it finally worked out.

I simply connected the inputs to the line in port on the sound card rather than the mic in port.

As per the 1V well, maybe something went wrong with my meter. Thanks anyway.

simply for the interest

the mic port has three connections (it is a stereo socket). the three connections are ground, signal, and power. You probably connected the input to the power, instead of the signal (this is why it worked when you connected it to line-in, because there is two 'signals'). If you had simply switched which connection the input was connected to (changed from what is uually refered to as 'left' and 'right') it would have worked.

Tim

Thank you.

This might be very helpful since i do not have a line in port on the sound card on my laptop . If you are right, it means I can use the laptop to run the software and still get the desired result.

I will try it out Now.

Thanks a million.